This invention relates to novel resins and filler materials for restorative dentistry. Depending on resin and filler content, the resins and fillers may be used as crown and bridge materials, either with or without an alloy substrate; or as reconstructive materials, bioprostheses, restorative materials, filling materials, inlays, onlays, laminate veneers, dental cements, dental adhesives and the like.
In recent years, materials used for dental restorations have comprised principally acrylate or methacrylate resins. Typical acrylate resinous materials are disclosed in U.S. Pat. No. 3,066,112 to Bowen, U.S. Pat. No. 3,179,623 to Bowen, U.S. Pat. No. 3,194,784 to Bowen, U.S. Pat. No. 3,751,399 to Lee et al. and U.S. Pat. No. 3,926,906 to Lee et al. An especially important methacrylate monomer is the addition product of bisphenol A and glycidyl methacrylate, 2,2′-bis[4-(3-methacryloxy-2-hydroxy propoxy)-phenyl]-propane (hereinafter abbreviated “Bis-GMA”). Polyurethane dimethacrylates (hereinafter abbreviated PUDMA) are also commonly used principal monomers in dental restorative materials. Since Bis-GMA is highly viscous at room temperature, it is generally diluted with an acrylate or methacrylate monomer having a lower viscosity such as trimethylolpropyl trimethacrylate, 1,6-hexanedioldimethacrylate, 1,3-butanediol dimethacrylate, and the like. Other dimethacrylate monomers, such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, and tetraethylene glycol dimethacrylate, are also in general use as diluents.
When these acrylic resinous materials were first developed, they were used for dental restorative purposes unfilled, that is, without the presence of any other organic or inorganic component. However, because acrylic materials exhibit high coefficients of thermal expansion relative to the coefficient of thermal expansion for the tooth structure, these unfilled substances proved to be less than satisfactory. The disparity in thermal expansion, coupled with high shrinkage upon polymerization, resulted in poor marginal adaptability and ultimately led to secondary decay. Furthermore, the wear and abrasion characteristics and the overall physical, mechanical, and optical properties of these unfilled acrylic resinous materials were quite poor. Composite dental restorative materials containing methacrylate resins and fillers were thus developed, the fillers generally comprising inorganic materials based on silica, silicate glass, or quartz. Particularly suitable improved inorganic filler materials include those disclosed in commonly assigned U.S. Pat. No. 4,547,531 to Waknine, and U.S. Pat. No. 4,544,359 to Waknine.
There are now available resins that exhibit high diametral tensile strength, excellent optical properties and polishability, and low water sorption while at the same time complying with all of the requirements specified in ADA Specification No. 27 for Direct Filling Resins. Exemplary materials comprise monomers and polymers disclosed in commonly assigned U.S. Pat. No. 5,276,068 to Waknine and U.S. Pat. No. 5,444,104 to Waknine Such materials make use of a novel polycarbonate dimethacrylate (PCDMA) which is the condensation product of two parts of hydroxyalkylmethacrylate of the formula H2C═C(CH3)C(O)O-A-OH, in which A is a C1-C6 alkylene, and 1 part of a bis(chloroformate) of the formula ClC(O)—(OR)n—OC(O)Cl, in which R is a C2-C5 alkylene having at least two carbon atoms in its principal chain, and n is an integer from 1 to 4. This polycarbonate dimethacrylate imparts excellent strength to the cured resin, but it is somewhat costly. Another advantageous resin having lower water sorption characteristics, as disclosed in U.S. Pat. No. 5,969,000, is an ethoxylated bisphenol A dimethacrylate (EBPDMA) having the structure CH2═C(CH3)CO2(C2H4)xC6H4C(CH3)2C6H4(C2H4)yO2CC(CH3)═CH2, wherein x+y is an integer from 1 to 20, and preferably from 2 to 7. While such resins are well suited for their intended purposes, there is a perceived need in the art for dental resin materials with even more advantageous physical properties, particularly strength, water sorption, and wear.
Current dental restorative composites are continuously being developed to improve strength, wear resistance, and other chemical and physical working and handling properties. One of the main challenges associated with achieving an optimal composite is the development of improved filler compositions. Numerous attempts have been made in recent decades to create optimal fillers suitable for dental composites. These efforts have included reducing the size of glass/ceramic fillers, creating sol-gel spherical microparticles, surface modification of particles/fibers, and treatment of amorphous silica particles. Although some of these efforts have provided some improved properties of dental composites, there remains a continuing need for improved, highly functional filler material.
This invention further relates to novel filler materials that overcome the disadvantages associated with dental ceramic fillers based on non-silicate metallic compounds, such as zirconium oxide, aluminum oxide, ytterbium fluoride, etc. Generally, dental ceramic fillers based on non-silicate metallic compounds are not considered good fillers for a dental resin composite, especially when the amount of those fillers added into a dental resin restorative composite material is large, although the filler themselves are usually hard and strong in nature and having the advantage of being more radioopaque due to the higher atomic numbers. This is because the interface between the polymeric resin matrix and the non-silicate ceramic fillers are usually weak due to the fact that the conventional silane surface treatment on those fillers is not chemically compatible and therefore, the silane surface coupling effect to the filler surfaces is minimal. Thus, there is a need for improved dental filler materials based on non-silicate metallic compounds that provide improved physical properties, radio-opacity, that are easily silanized by conventional methods to achieve a good dental composite.